Optimization Of A Vapor Recovery Unit

ABSTRACT

This vapor control logic system is for optimizing terminal loading capacity by controlling load rack fuel dispensing with a vapor recovery unit (VRU) to prevent undesirable shutdown of fuel dispensing at terminal facilities.

CROSS REFERENCE TO RELATED APPLICATION

The present patent application is based upon and claims the benefit of provisional patent No. 61/939,427, filed Feb. 13, 2014.

FIELD OF THE INVENTION

The present invention relates to optimizing terminal loading capacity by controlling load rack fuel dispensing to prevent undersirable shutdown of fuel dispensing at terminal facilities.

BACKGROUND OF THE INVENTION

An oil depot (sometimes referred to as a tank farm) is an industrial facility for the storage of oil and petrochemical products. Oil depots often include terminals where the oil or petrochemical product is dispensed into road tankers or other methods of transportation such as barges or pipelines. Products dispensed from an oil terminal are generally in their final form and are suitable for delivery to customers. The petrochemical products dispensed at a terminal are often referred to as wholesale fuel.

Terminal technology has remained largely unchanged for many years. The road tanker, or tanker truck, enters the terminal to obtain wholesale fuel. An operator determines the type of fuel and additives desired and the tanker truck is connected to the terminal. The vast majority of terminals now use a bottom fill system wherein the fuel fill line attaches to the bottom of the tanker and fills the tanker from the bottom up. When the tanker truck is filling, fuel vapors are produced which must be safely disposed of. These fuel vapors may be combusted or recovered with both methods having advantages and disadvantages. When a tanker truck is filling, a vapor vent line is connected to a tanker which transports the fuel vapors from the tanker truck to its final destination, either to a recovery unit to be recovered or to a combuster to be combusted.

Many terminals have begun using a vapor recovery unit (hereinafter VRU) to recover the fuel vapors which are produced when filling a tanker truck, or other fuel transportation vehicle. A typical VRU unit has at least two adsorber vessels filled with activated carbon, a vacuum pump or other source of vacuum, an absorber vessel, a return pump and a plurality of valves. The adsorbers are properly piped and valved so that one adsorber is currently receiving vapors while the other adsorber is in a regeneration mode. When the loading process begins at the terminal, vapors are transported to the active adsorber where they are adsorbed, usually by activated carbon. Once an adsorber vessel is saturated or on a set cycle time, the vessel is switched to a regeneration mode and the vapors are directed to the second adsorber vessel while the first adsorber regenerates.

Regeneration occurs when the adsorbed fuel vapor is removed from the activated carbon so that the carbon in the adsorber vessel is regenerated and capable of adsorbing more fuel vapors. The fuel vapor is commonly removed by vacuum and purge air stripping. A vacuum pump extracts the fuel vapor from the saturated adsorber and transfers it to an absorbtion column. The absorption column vessel contains a packing material to increase the efficiency of the absorption process. The fuel vapors from the adsorber flow up through the absorbtion column, while liquid fuel flows down through the packing. The liquid fuel absorbs the vapors retained in the packing. The now liquefied fuel is pumped to the storage tank. All fuel vapors not absorbed in the absorption column are returned by use of a recycle line to the adsorber to be recovered.

The VRU is typically run in fifteen-minute cycles wherein one adsorber is online and accepting fuel vapors while the other adsorber is offline and in regeneration mode. Some terminals operate at full capacity putting a larger load on the VRU. It has been found that, if the limiting factor is the VRU, the adsorbers commonly cannot regenerate as quickly as they are saturated. Therefore, the terminal load rack capacity exceeds the VRU capcity. If the VRU is run at full capacity for an extended period of time the VRU may go into total shutdown where both adsorbers regenerate and no fuel can be dispensed at the terminal.

Therefore it is an object of this invention to maximize the terminal loading capacity by controlling the load rack fuel dispensing with the VRU performance outputs to prevent undesirable shutdown of the fuel dispensing at terminal facilities.

SUMMARY OF THE INVENTION

One of the key factors on how much fuel can be dispensed at a terminal, is dependent on the VRU capacity. The following factors are evaluated to determine the VRU capcity, but are not limited to: the VRU design and equipment, ambient temperature, product temperature, the product type being loaded, the product that was previously loaded, and the rate of loading. The current method evaluates of these factors over a given year to establish a theoretical static VRU capacity. Because these inputs are a historical representation of performance of the fuel terminal and the VRU the capacities are set and cannot be optimized with real time performance data.

A current typical design logic of the system is as follows:

-   -   The VRU operation is initiated when a predetermined number of         tanker trucks have been loaded or runs continuously,     -   One of the VRU adsorber unit enters a regeneration cycle for the         first time, while the other adsorber is being loaded,     -   The VRU begins its cycle wherein it then regenerates every         fifteen minutes, first regenerating one adsorber and then the         other. This cycle continues until loading activity has ceased at         the terminal or the vapor recovery units are fully regenerated.         When dispensing fuel above the capacity of a VRU, the unit is         not capable of fully regenerating quickly enough to maintain         pace with the rate of fuel being dispensed. Therefore, the vapor         levels build up within the adsorber units resulting in peak         saturation and shutdown of the fuel dispensing.

Many vapor recovery units now utilize a continuous emissions monitor (OEM) to monitor and analyze the effluent stream exiting the top of the adsorber units. These continuous emission monitors provide data, which can be coupled with other data (such as ambient temperature, product temperature, product being loaded, product that was previously loaded, and loading rate) to optimize the VRU and the load rate such that the operating capacity would not be exceeded which currently results shut down situation. When the loading process begins at the terminal a signal is sent to the VRU to determine whether it can accept vapors. It will indicate the VRU can accept vapors as long as it is not at a 100% saturation state, If loading begins, while the VRU is near saturation, it rapidly becomes saturated and regeneration is activated. The present invention optimizes the utilization of all data points to determine VRU saturation levels, reduce the flow rate of fuel into the tanker truck, thereby avoiding maximum saturation. Thus ensuring the VRU remains in service and never becomes fully saturated, allowing more fuel to be dispensed at the terminal throughout the given time period.

Other objects and advantages of the present invention will become apparent to those skilled in the art upon a review of the following detailed description of the preferred embodiments and the accompanying drawings.

IN THE DRAWINGS

FIG. 1 is a top plan view of a vapor recovery unit of the present invention.

FIG. 2 shows a vapor control logic system.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 1 a tanker truck 12 enters a terminal 10 and fuel is dispensed into tanker truck 12 from a storage tank 14. Fuel vapors are recovered from tanker truck 12 and transported to a vapor recovery unit (VRU) 16. The fuel vapors may travel through condensation collection unit 18 prior to arriving at VRU 16. The condensation collection unit 18, however, is not integral to the present invention. A typical VRU 16 has two adsorbers vessels 20 and 22 which are identical and preferably contain activated carbon to capture the fuel vapors. One adsorber vessel is on-line while the second adsorber is regeneration mode. The second adsorber, during regeneration mode, is closed off from fuel vapor line 24 and all fuel vapors flow to the on-line adsorber. For the purposes of this illustration adsorber 20 will be on-line while adsorber 22 is in regeneration. The fuel vapors flow into adsorber 20 from loading tanker truck 12. When adsorber 20 is in fueling mode, the top 26 of the adsorber is vented to the atmosphere. A continuous emissions monitor 28 (CEM) is attached to monitor and analyze the effluent stream exiting the adsorber. After a predetermined period of time, amount loaded, or saturation level is reached, adsorber 20 is switched into regeneration mode and adsorber 22 is placed on-line to accept fuel vapors.

During regeneration the fuel vapors are brought from adsorber 20, using a vacuum pump 30, to an absorber tower 32. The absorber tower 32 contains packing such as wherein the fuel vapors flow up through the packing while liquid fuel flows down through the packing causing the liquid fuel to absorb the fuel vapors. Any remaining fuel vapors are returned to the condensation collection unit 18 or the adsorption tank currently on line, while the liquid fuel is transferred to the storage tank 14 to be loaded.

The present invention utilizes real-time data points to optimize the operations of the VRU 16 and prevent a fueling shutdown. Such data includes but is not limited to: real-time ambient temperature, product temperature, load rate, product being loaded, product previously loaded, and the effluent rates from the adsorbers.

FIG. 2 shows vapor control logic system 40. Logic system 40 includes data processor 42 and controller 44. Vapor control logic system 40 uses data processor 42 to collect and analyze the performance of VRU 16 and fuel dispensing in real-time. Data processor 42 is coupled to controller 44 configured to adjust the flow rate at the load rack based on the parameters, data points and desired factors in real-time. Continuous emissions monitor 28 utilizes data processor 42 and controller 44, to adjust the flow rate at the load rack to ensure that VRU 16 does not reach a shutdown situation.

The present invention uses a data processor to collect and analyze the performance of the VRU and fuel dispensing in real-time. The data processor is coupled to a controller which is capable of adjusting the flow rate at the load rack based on the parameters, data points and desired factors. As the VRU approaches capacity limits, monitored by the CEM, the data processor, using the controller, will adjust the flow rate at the load rack to ensure that the VRU does not reach a shutdown situation. The invention provides that the fuel flow rate can be reduced such that VRU can perform at an equivalent pace. In the preferred embodiment the data processor will prevent the VRU from shutting down by reducing the fuel flow rate to a level that is equal to or below the VRU capacity at any given time. The optimal fuel flow rate will be determined utilizing the real-time data points such as ambient temperature, product temperature, product being loaded, product previously loaded and the emissions from the VRU.

The above detailed description of the present invention is given for explanatory purposes. It will be apparent to those skilled in the art that numerous changes and modifications can be made without departing from the scope of the invention. Accordingly, the whole of the foregoing description is to be construed in an illustrative and not a limitative sense, the scope of the invention being defined solely by the appended claims. 

We claim:
 1. A method for optimizing terminal loading capacity by controlling load rack fuel dispensing with a vapor recovery unit (VRU) to prevent undesirable shutdown of fuel dispensing at terminal facilities comprising the steps of: providing a vapor recovery unit (VRU) comprising a first bed of adsorbent and a second bed of adsorbent; providing a vapor control logic system which controls flow direction of vapor captured from a transporting vessel being loaded in response to user inputs; adsorbing vapor from an air-volatile liquid vapor mixture on the first bed of adsorbent, measuring a total amount of the vapor adsorbed by the first bed of adsorbent; comparing the total amount of vapor adsorbed on the first bed of adsorbent to a first predetermined value that is less than 100% of the first bed's adsorbance capacity; and regenerating the first bed of adsorbent and adsorbing vapor from said air-volatile vapor mixture on the second bed of adsorbent upon reaching a first predetermined value whereby regeneration may be initiated before vapor breakthrough; controlling operation of the VRU with the vapor control logic system on-line in response to user inputs; wherein the step of controlling on-line is carried out with real time optimization (RTO) processing.
 2. A process according to claim 1 wherein the step of control on-line utilizes advance process control (APC) technology to optimize (RTO) operation of the VRU.
 3. A process according to claim 1 wherein the vapor control logic system is configured to activate regeneration if the VRU is near saturation.
 4. A process according to claim 1 wherein the user inputs are VRU design and equipment, ambient temperature, product temperature, product type being loaded, product previously loaded, or rate of loading.
 5. A process according to claim 1 wherein the vapor control logic system utilizes real-time data points to optimize the operations of the VRU and prevent a fueling shutdown.
 6. A process according to claim 1 wherein the vapor control logic system uses a data processor to collect and analyze the performance of the VRU and fuel dispensing in real-time.
 7. A process according to claim 6 wherein the data processor is coupled to a controller configured to adjust the flow rate at the load rack based on the parameters, data points and desired factors in real-time.
 8. A process according to claim 7 wherein continuous emissions monitor utilizes the data processor and the controller, to adjust the flow rate at the load rack to ensure that the VRU does not reach a shutdown situation.
 9. A process according to claim 1 wherein the vapor control logic system is configured to provide that the fuel flow rate can be reduced such that VRU can perform at an equivalent pace.
 10. A process according to claim 6 wherein the data processor is configured to prevent the VRU from shutting down by reducing the fuel flow rate to a level that is equal to or below the VRU capacity at a given time. 